1. Field of the Invention
The present invention relates to a touch panel, more specifically, to a touch panel configured so that a difference becomes less obvious in thickness between upper and lower electrode connecting portions and a sealing agent portion.
2. Description of the Related Art
A conventional touch panel will be described with reference to FIGS. 4A and 4B.
FIG. 4A is a perspective view showing a conventional touch panel in the state of disintegrating an upper substrate and a lower substrate. As shown in the drawing, the conventional touch panel includes an upper substrate 1, a lower substrate 2, a transparent conductive film 11 formed on one surface of the upper substrate 1, a transparent conductive film 21 formed on one surface of the lower substrate 2, two upper position detection electrodes 12 formed on the upper substrate 1 so as to face each other, two lower position detection electrodes 22 formed on the lower substrate 2 so as to face each other, extending electrodes 31, 32, 33 and 34 which extend to the outside of the touch panel (hereinafter referred to as extending electrodes), the extending electrode being formed on the lower substrate 2, and a sealing agent 4 for attaching peripheral edges of the upper substrate 1 and the lower substrate 2 together.
A glass plate is used for the upper substrate 1, and the transparent conductive film 11 is formed on the entire surface thereof except the peripheral edges. Moreover, the upper position detection electrodes 12 for detecting a position in an X direction are provided along an upper edge and a lower edge of the transparent conductive film 11.
A glass plate is used for the lower substrate 2, and the transparent conductive film 21 is formed on the entire surface thereof except the peripheral edges. Moreover, the lower position detection electrodes 22 for detecting a position in a Y direction are provided along a left edge and a right edge of the transparent conductive film 21. The extending electrodes 31 and 33 are extended from the lower position detection electrodes 22, and the extending electrode 32 and 34 are extended by connecting lower electrode connecting portions 36 provided on another ends thereof to the upper position detection electrodes 12 of the upper substrate 1.
Each upper electrode connecting portion 16 provided on an end of each upper position detection electrode 12 and each lower electrode connecting portion 36 provided on another end of each of the extending electrodes 32 and 34 are formed in positions corresponding to corner portions of the upper substrate 1 which have relatively large spaces.
The upper substrate 1 and the lower substrate 2 of the above-described configuration are arranged such that the transparent conductive films 11 and 21 are opposed to each other, and are bonded together at the peripheral edges outside the upper position detection electrodes 12 and the lower position detection electrodes 22 by use of the sealing agent 4.
Next, FIG. 4B is a cross-sectional view taken along the E-E line in FIG. 4A when the upper substrate 1 is bonded to the lower substrate 2. As shown in the drawing, the upper electrode connecting portion 16 and the lower electrode connecting portion 36 are connected so as to overlap each other in terms of a direction of pressurization by use of an unillustrated conductive adhesive.
The above-described touch panel is configured such that when an arbitrary point is pressed with a finger, a pen or the like, the transparent conductive film 11 of the upper substrate 1 and the transparent conductive film 21 of the lower substrate 2 contact each other at that point. Here, a resistance value of the transparent conductive film 11 is detected and the x-coordinate of the point can be thereby identified. Meanwhile, a resistance value of the transparent conductive film 21 is detected and the y-coordinate of the point can be thereby identified.
When the pressing operation is stopped, the transparent conductive film 11 of the upper substrate 1 and the transparent conductive film 21 of the lower substrate 2 are detached and the touch panel is set to off-state. This technology is described for instance in Japanese Unexamined Patent Publication No. 2003-316517 (claim 4, FIG. 2).
Another conventional touch panel will be described with reference to FIGS. 5A to 5C.
FIG. 5A is a perspective view showing another conventional touch panel in the state of disintegrating an upper substrate and a lower substrate. This conventional touch panel has the same configuration as the touch panel shown in FIGS. 4A and 4B except that the positions of the upper electrode connecting portions 16 of the upper position detection electrodes 12 on the upper substrate, the positions of the lower electrode connecting portions 36 of the extending electrodes 32 and 34 on the lower substrate 2, and the shapes of the lower electrode connecting portions 36 are different. Here, the portions corresponding to those in FIGS. 4A and 4B are designated by the same reference numerals and detailed description thereof will be omitted.
As shown in the drawings, the lower electrode connecting portions 36 of the extending electrodes 32 and 34 are provided in the vicinities of the portions where the sealing agent 4 is formed inside the extending electrodes 32 and 34. Meanwhile, the upper electrode connecting portions 16 of the upper substrate 1 are extended to the position corresponding to the upper parts of the lower electrode connecting portions 36.
FIG. 5B is an enlarged view of the upper and lower electrode connecting portions 16 and 36 when the upper substrate 1 and the lower substrate 2 in FIG. 5A are bonded together. As shown in the drawing, the lower electrode connecting portion 36 of the lower substrate 2 formed into a shape to pinch the upper electrode connecting portion 16 of the upper substrate 1. The upper electrode connecting portion 16 of the upper substrate 1 is disposed in an opening of the lower electrode connecting portion 36, and is connected thereto by use of an unillustrated conductive adhesive.
FIG. 5C is a cross-sectional view taken along the F-F line in FIG. 5B. As shown in the drawing, the lower electrode connecting portion 36 is connected so as to pinch the upper electrode connecting portion 16. Accordingly, the lower electrode connecting portion 36 and the upper electrode connecting portion 16 are configured not to overlap in the pressing direction of the upper and lower substrates 1 and 2. This technology is described for instance in Japanese Unexamined Patent Publication No. 2004-178106.
As described above, in the former conventional touch panel, the upper and lower electrode connecting portions 16 and 36 are provided in the positions corresponding to the corner portions of the upper substrate 1. For this reason, it is possible to ensure large spaces for connecting the upper electrode connecting portions 16 to the lower electrode connecting portions 36, and thereby to connect the upper and lower electrode connecting portions 16 and 36 easily.
However, due to the above-described configuration, there is a large gap between a thickness which is caused by overlapping the upper electrode connecting portion 16 on the lower electrode connecting portion 36, and, a thickness of the sealing agent 4 formed outside thereof. When the upper and lower substrates 1 and 2 are attached together by pressurization and baking in this state, stress concentration would occur at the portions of the upper and lower electrode connecting portions 16 and 36, which would cause cracks on the upper substrate 1 made of glass.
Moreover, when attaching the upper and lower substrates 1 and 2 together by pressurization and baking, it is difficult to control the pressure to be applied to the upper and lower electrode connecting portions 16 and 36 and to adjust the amount of the sealing agent 4 to be formed relevantly. For this reason, the width of the sealing agent 4 would become uneven in the vicinities of the upper and lower electrode connecting portions 16 and 36, which would cause adhesion failures.
Meanwhile, in the latter conventional touch panel described above, the upper and lower electrode connecting portions 16 and 36 are provided in the vicinities of the portions where the sealing agent 4 is formed inside the extending electrodes 32 and 34 of the lower substrate 2. For this reason, the gap between the thickness of the upper and lower electrode connecting portions 16 and 36 and the thickness of the sealing agent in the vicinity thereof becomes less obvious when attaching the upper and lower substrates 1 and 2 together. Accordingly, it is possible to reduce cracks at the portions of the upper and lower electrode connecting portions 16 and 36, which occur at the time of attaching the upper and lower substrates 1 and 2 together by pressurization and baking.
However, as the lower electrode connecting portion 36 is formed into the shape so as to pinch the upper electrode connecting portion 16, it is necessary to form the width of the lower electrode connecting portion 36 wider than the upper electrode connecting portion 16. For this reason, the area of the upper and lower electrode connecting portions 16 and 36 is increased and an operating region of the touch panel is reduced as a consequence.
Moreover, by repeating the pressing operation on the upper substrate 1, connection between the upper and lower electrode connecting portions 16 and 36 becomes unstable, whereby it is difficult to achieve identification of the pressed position.